Salt-sensitivity or salt-dependent elevations in blood pressure are evident in a majority of the human population. Renal defects in the control of sodium excretion are known to be major contributors to the development of salt-dependent hypertension. Work conducted by each of the Project Leaders over the past 10 years has provided important Information about the powerful role of the renal endothelin (ET- 1) system in the control of sodium excretion, renal hemodynamics, and blood pressure indicating that the endothelin system rivals the renin-angiotensin system in physiological significance. This includes important evidence that a high salt diet, even without hypertension, has a significant influence on renal hemodynamic function. Our studies have led us to hypothesize that the ETB receptor functions as a counter-balance to the powerful vasoconstrictor and pro-hypertensive actions of the ETA receptor. However, there is simply not enough information available about the specific conditions that determine the activity of these receptor systems. The current proposal builds on studies demonstrating that the ETA receptor plays a role in promoting hypertension and associated end-organ damage while a lack of ETB receptor function results in increased sensitivity to salt-induced hypertension. Therefore, the goal of the current Program Project is to determine the physiological actions of ET-1 using an array of experimental approaches ranging from the gene level to whole animal models to comprehensively explore the pathways regulating ET-1 activity in the kidney. The current Program is made of four Projects. Each project explores a unique aspect of the endothelin system in terms of both hemodynamics and tubular function and will elucidate the receptor subtype specific actions on inflammation, oxidative stress, renal hemodynamics and tubular function; a particular emphasis is on factors that influence the control of sodium excretion and blood pressure. These studies are expected to provide important new insight into a major system that regulates renal sodium excretion. In particular, this Program will investigate a full range of mechanisms that control ET-1 release and receptor specific actions in order to provide clinically relevant information.